Many have had similar issues with wanting to run GUI with su privileges. More recently I have looked into the lingering open terminal window. After searching this is what worked for me.

- my usage is invoking GUI with SU from the term and/or a shell script from ~/bin using aliases. 

***
***GUI privilege escalation of "su" or "sudo" is not recommended and should never be done with out knowledge of the risks of what your doing.***
***
- pkexec can be obtained by the following:

 sudo apt install policykit-1

***
- Edit the bottom of this file to where it looks likes this:

 sudo nano /usr/share/polkit-1/actions/org.freedesktop.policykit.policy

- yours should look like this:

 <action id="org.freedesktop.policykit.lockdown">

 <description>Configure lock down for an action</description>

 <message>Authentication is required to configure lock down policy</message>

 <defaults>

 <allow_any>auth_admin</allow_any>

 <allow_inactive>auth_admin</allow_inactive>

 <allow_active>auth_admin</allow_active>

 </defaults>

 <annotate key="org.freedesktop.policykit.exec.path">/usr/bin/pklalockdown</annotate>

 </action>
***

- After that try:

 pkexec gedit 
***

***Adding a custom bin path to terminal:***
- The Standard is to store users shell programs in 

 /home/$USER/bin
or

 ~/bin
*These are the same location the first is the full path to file the second is short hand for

 /home/$USER/bin

- To add your user /bin to your $USER $PATH simply

 mkdir /home/$USER/bin
- terminal will now recognise your shell scripts or programs located in

 ~/bin

Example:

 $/path/to/file.sh 
Becomes:

 $file.sh

ADD this to .bashrc
 
 

 

> export PATH=$PATH:$HOME/bin
> 
> Where "$HOME/bin" is the directory I assume you want to add. This
> change is only temporary (it works only in the current session of the
> shell) to make it permanent add the previous line to your .bashrc file
> located in your home directory.



- I prefer this method of privilege escalation for gui apps because i can just pkexec in a shell script to run multiple programs and have the option to save credentials temporarily. 

- you then can try and add an alias to ~/.bash_aliases:

 echo 'alias gedit="pkexec gedit"' >> ~/.bash_aliases